ENGLISH ABSTRACT: Mealiness, a soft, dry textural disorder of ‘Forelle’ pear (Pyrus communis L.), is a problem for the South
African fruit export industry. Soft, dry textural disorders seem to be related to changes in cell wall
breakdown. The aim of this work was, therefore, to investigate the occurrence of mealiness‐associated
changes in the cell wall and elucidate the mechanism by which mealiness occurs in ‘Forelle’ pear, as well as
to characterise cell wall changes occurring during normal ripening.
Mealy ‘Forelle’ tissues had significantly lower total galacturonic acids associated with the middle lamella
(water‐ and CDTA‐soluble fractions). The water‐soluble pectin of mealy tissues was depolymerised at an
earlier stage of ripening. The widespread disintegration of cell‐to‐cell adhesion in mealy cell walls only,
suggests that the middle lamella and the plasmodesmata are more broken down. In mealy ‘Forelle’ tissues
there was no indication of less broken down high molecular weight polyuronides in the CDTA fraction,
normally associated with these dry, soft textures. The pectins from mealy tissues were more broken down
and both mealy and non‐mealy tissue polyuronides depolymerised. Furthermore, there was a lack of light
toluidine staining in the larger air spaces, which would indicate such water‐insoluble pectins. These data
suggest that the formation of high molecular weight pectate gels is unlikely in mealy ‘Forelle’ pear. The
slight increase in the galactose content in mealy tissues in CDTA‐ and Na2CO3‐soluble fractions and slight
decrease in the 1 M KOH glycan fraction during later stages of ripening (6+11, 9+7, 9+11; weeks at ‐0.5°C
plus days at 15°C) may indicate that galactose loosely interlinked into the glycan fraction broke down
sooner for mealy tissues. This didn’t increase molecular size profiles in the CDTA fraction. Arabinose
content was slightly higher in the 4 M KOH fraction and slightly lower in mealy tissues of water‐ and
CDTA fractions. This did not influence the molecular weight of the glycans compared to those in the nonmealy
tissues. ‘Forelle’ data therefore seem to be more congruent with a decrease in intercellular adhesion
as the mechanism by which mealiness occurs, rather than the formation of high molecular weight pectins
taking up the cellular fluid.
‘Forelle’ pear water‐soluble pectin content increases with increased ripening. High amounts of watersoluble
pectin and low amounts of Na2CO3‐soluble pectin suggests that solubilisation of
rhamnogalacturonan‐I pectins must have taken place during early ripening (at a fruit firmness of > 4.7 kg
(7.9mm tip). Galactose and glucose in the pectin fraction dramatically decreased after fruit ripened to a
firmness of 4.5 kg, whereafter they remained unchanged. This was also the period in which fruit softened
the most and the biggest increase in pectin water‐solubility occurred. It is not known whether these events
are coincidental, or linked causally. Rhamnose and arabinose extractability increased in the water fraction
and xylose, fucose and mannose increased in glycan fractions with ripening. The biggest changes in
polyuronide solubilisation and depolymerisation occurred in water‐ and CDTA fractions between storage
and ripening durations of 3+7 (4.7 kg) and 6+4 (2.7 kg).